Other Angiographic Sudies

The previous section dealt with angiographic studies of the aorta and systemic arteries. Many of these techniques are also applicable to evaluation of the pulmonary circulation, splanchnic veins and the central and peripheral systemic veins. These procedures assume increasing importance as the tools and techniques of arterial interventions are brought to bear on diseases effecting the venous system.

Pulmonary Angiography

Pulmonary angiography is the gold standard for diagnosing pulmonary embolism (PE). Despite its importance in this life threatening condition, pulmonary angiography is significantly underutilized and often employed improperly. Any patient for whom there is a high clinical suspicion of PE should first have a nuclear medicine lung scan (V/Q scan). The clinically useful results from that examination are "normal" and "high probability". Any other result mandates a pulmonary angiogram if it is within 48 hours of the patient's acute episode. After 48 hours the sensitivity of pulmonary angiography drops significantly in about 85% of patients, and a normal study does not rule out a PE with subsequent clot lysis. If the pulmonary angiogram cannot be done within the 48 hour window of sensitivity, suggestive evidence may be obtained by a follow up V/Q scan.

Once the decision to proceed to pulmonary angiography is made, the search for an embolus must be exhaustive. A complete examination may include both main and selective left and right pulmonary artery injections in multiple projections, and may subject the patient to a contrast load of more than 300ml. Obviously, the procedure can be interrupted when the first positive angiographic series is completed.

Other indications for pulmonary angiography include chronic recurrent PE to assess obliterative changes in the arterial tree, and in the work-up of hemoptysis following a negative bronchial arteriogram (i.e. pulmonary arteriovenous fistula as in Osler-Weber-Rendu syndrome).

Relative contraindications to pulmonary angiography are severe pulmonary hypertension, left bundle branch block, and congestive heart failure. Catheter irritation of the intraventricular septum may induce right bundle branch block. In patients with pre-existing LBBB, this may result in complete heart block. This contraindication can be overcome by the prophylactic placement of a temporary pacemaker. Patients having pulmonary hypertension without a significant elevation in the right ventricle end diastolic pressure will generally tolerate selective pulmonary angiography. With decompensation of the right ventricle (i.e. RVEDP > 20 mmHg), even selective pulmonary angiography places the patient at risk for sudden death. These patients can be studied with sub-selective balloon occlusion technique, but such procedures are exceedingly tedious, time consuming, and difficult for the patient.

Peripheral Venography

Deep venous thrombosis (DVT) is a potentially life-threatening condition with a relatively high incidence in hospitalized patients and in those with indwelling central venous catheters. Suspected DVT is the most frequent indication for venography (phlebography, venous angiography), and venography remains the gold standard for making that diagnosis. Nevertheless, compression ultrasound with Doppler has made significant advances recently, and, in most cases, state-of-the-art venous ultrasound is an entirely satisfactory noninvasive means of diagnosing DVT of the popliteal and femoral veins. However, the sensitivity of ultrasound for detecting DVT in the calf is low.

In current medical practice there is controversy concerning treatment of isolated calf DVT. Those favoring treatment cite a decreased incidence of postphlebitic syndrome, a disease which has significant life long morbidity. On the other hand, isolated calf DVT rarely imposes a significant threat of fatal pulmonary embolism, and anticoagulation does have a significant (10-15%) risk of bleeding complications. Thus, many physicians favor following calf DVT and treating only if the thrombus propagates into the popliteal or femoral veins. The therapeutic decisions become even more complex and controversial in cases of iliofemoral and femoropopliteal DVT. There is now mounting evidence that, in many patients, thrombosis involoving these large conducting veins should be treated agressively with thrombolytic therapy in addition to anticoagulation. In these cases, venous angiography is an integral part of the treatment.

Based on the above considerations, contrast venography of the lower extremities should be preceded by venous ultrasound in nearly all cases. If the ultrasound study is positive, the diagnosis is made and therapy can be started. In such cases, contrast venography would be used only as an adjunct to venous thrombolysis. If the ultrasound is equivocal, or if it is negative but isolated calf DVT would be treated, then diagnostic contrast venography should be performed.

Upper extremity DVT occurs infrequently in the general population. Spontaneous axillosubclavian thrombosis may occur in muscular individuals during upper extremity exertion (effort thrombosis), or secondary to musculoskeletal impingement on the subclavian vein (thoracic inlet syndrome). More commonly, upper extremity DVT is secondary to an indwelling central venous access device such as a Hickman or Groshong catheter. Several studies have shown the incidence of central venous catheter related thrombosis to be 30-48%, although symptomatic thrombosis occurs in only 1-4% of patients. Ultrasound is satisfactory for evaluating the veins distal to the subclavian. However, the subclavian and brachiocephalic veins and superior vena cava are not amenable to sonographic study. Suspected thrombosis of these central veins requires contrast venography to confirm the diagnosis.

Visceral Venography

Indications for venography of the systemic visceral veins have decreased significantly since the advent of CT. In current practice, visceral venography is most often used in conjunction with other diagnostic tests. Hepatic venography with hepatic venous wedge pressure measurement is used to diagnose and assess the severity of portal venous hypertension. Renal venography is used with renal vein pressure gradient measurements to diagnose the Nutcracker Syndrome as a cause of hematuria. Venography performed in conjunction with transcatheter organ venous blood sampling is extremely useful in the work up or surgical planning for recurrent primary hyperparathyroidism and other hormonally active tumors of the endocrine glands, pancreas, kidneys, and gastrointestinal tract. In most cases, the organs potentially responsible for the hypersecretion are sampled directly. However, in the case of certain pancreatic or upper GI tumors such as gastrinoma, blood may be sampled from the hepatic vein during selective intraarterial injection of substances which promote secretion of the hormone. In the case of gastrinoma, secretin is injected into the gastroduodenal, hepatic, splenic, and superior mesenteric arteries while blood is sampled from the right hepatic vein. Assay results coupled with arteriographic mapping are then used to direct the surgical approach to the lesion.

Portal Venography

There are a variety of indications for study of the portal vein including suspected portal or splenic vein thrombosis, upper gastrointestinal tract bleeding, and in the preoperative work-up of upper abdominal malignancies such as pancreatic and hepatocellular carcinoma and metastatic involvement of the liver by various tumors. In most cases, angiographic study of the portal vein is done indirectly by way of contrast injections into the splenic or superior mesenteric artery, using a prolonged filming sequence (arterial portography). An older method of studying the splenic and portal veins is by direct percutaneous injection of contrast medium into the splenic pulp (splenoportography). Direct study of the portal vein and its tributaries is possible using either a percutaneous transhepatic approach from a right mid-axillary line or subxiphoid approach, or via a transvenous transhepatic approach from a right internal or external jugular access. This latter approach has recently evolved into a new procedure for creation of a portosystemic shunt which is described in a subsequent section.